The Rotation at Fanhouse has done some excellent statistical work on the teams headed to the playoffs. They even show graphically why there are about 8 teams with a legit shot at the title this year (and the Celtics stand out because of their defense). Of course, not all the stats are favorable.
Boston's a tasty jar of pickles. The Celtics have been, by far, the best NBA team this season. They have an absolutely dominant defense, as good as those the Spurs have presented during their title era. The offense is quite good, too -- #11 in the league.
But there are questions about Boston. As the quality of competition rises, ball-handling takes on increased import. And the Celtics are the absolute worst team in the league in turnover ratio (in other words, Boston's possessions end in turnovers more than any other team in the entire league ... even the Knicks). The Celtics also foul quite a bit, ranking #23 in defensive free throw rate. The playoffs are filled with exactly the sort of star players (LeBron, Kobe, Amare, Bosh, Billups, Gilbert, Manu) who draw a ton of fouls. (But yeah, Boston is tremendous.)